Blade strip and method of making the same



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T. H. FROST 1,942,025

BLADE STRIP AND METHOD OF MAKING' THE SAME Filed Jan. 5; 1931 PatentedJan. z, 19st PATENT oEFlc-E UNITED STATES BLADE s'rarr AND METHOD or'MAxnvG- 'rnE SAME '9 claims.

This invention relates to the manufacture vof fine edged blades offerrous alloys which may be hardened by the process of nitriding, thatis to say, by introducing nitrogen into, or causing it to combine with,the alloy. In one aspect my invention comprises a new and improvedmethod of making such blades in strip form. In another aspect itcomprises a novel blade strip herein shown as produced by the methodofmy l invention.

An important eld of use of my invention is in the production ofsafetylrazor blades of the thin flexible type which areadapted for use inholders wherein vthey are clamped for support.

16 In my prior Patent No. 1,827,780, granted October 20, 1931; I havedisclosed a safety razor blade with nitrided cutting edges, this beingthe first example in the art of a nitrided cutting edge, and fromanother standpoint the present invention 2) consists in a furtherdevelopment of my earlier invention above identified. v

The material I prefer to employ in the construction of the novel bladestrip, and in carrying out the improved method of my invention, is

a ferrous alloy containing a substantial amount of aluminum, usuallycombined with chromium or molybdenum or tungsten. An example of suchalloy is the material commercially known as nitralloy, and, while thismay be advantageously employed vin manufacture of fine edged blades,other ferrous alloys capable of being hardened -by the process ofnitriding and otherwise answering to the requirements of the blades tobe produced might be used.

In the nitriding operation as heretofore carried out, diiiiculty hasbeen experienced in preserving the shape of the blank in the hardenedblade on account of the fact that a local expansion of the materialapparently takes place in the nitriding operation, which tends to warpor distort the blade to an objectionable extent.

Blades nitrided throughout their entire area,

particularly thin iiexible blades, are usually too brittle for practicalpurposes. This is particu- 5 larly true of such an article as a flexiblerazor blade which is commonly maintained in a position of pronouncedtransverse curvature when in use, and must therefore be capable ofwithstanding appreciable bending stress;

I have discovered that if the nitriding operation is carried out upon ablank which is in the meantime maintained under tension theobjectionable tendency to distort, above discussed, is eliminated orreduced to a negligible amount. My invention accordingly ischaracterized by the step of subjecting a strip or'a blank of anitridable ferrous alloy to the combined action of heat and ammonia, andsimultaneously maintaining the strip or blank under tension. In otherWords, I propose to effect the nitriding operation while the strip ismaintained in a state of tension, and under these conditions thereadjustment of the nitralloy in the nitriding operation does notproduce the distortion of the at strip which would otherwise occur. Theamount of tension to which the blank is subjected may be varied withinconvenient limits, but preferably will not exceed the elastic limit ofthe alloy at the degree of heat to which it is subjected.

An important advantage of the method above outlined is that it lendsitself to continuous-process operation 'and therefore may be carried outwith marked economy, particularly in those cases where the material tobe treated is available in long strips or ribbons. Under theselconditions the tensioned strip may be moved through a heated armnoniacontainer at such a rate as to cause Vthe nitriding operation toprogress to the desired point during the passage of the strip throughthe container. 'I'he process of my invention may also 80 .beadvantageously applied to the production of strips or blanks which arenitrided in portions only of their entire area. For example, in themanufacture of safety razor blades it is desired to nitride only thenarrow marginal zone including the cutting edge, and to leave the bodyof the blank unnitrided, and consequently duttile in its character.'Ihis may be accomplished in accordance with another feature of myinvention by protecting the strip or blank in any desired 'man- 90 nerbetween its marginal edges. As herein shown the body of the strip isprotected by a` coating or plating impervious to nitrogen and theferrous alloy is exposed only in the narrow marginal zones of the strip.It will be understood, however, that it would be within the scope of myinvention to protect the body of the strip by any means which iseffective to prevent or reduce the nitriding operation in selectedareas.

My invention may be practiced in the treatment of continuous strips or'ribbons of ferrous alloy, or of strips in which the outline of theblanks has been partially outlined by punching or trimming, or whichhas'been perforated or otherwise partially prepared for the ensuingsteps in its manufacture. For purposes of illustration I I have hereinshown a blade strip having asuccession of blade areas set off herein byspaced edge notches in the strip and'in the nitriding operation thenarrow edge zones, included individ- 11 Astrips of the characterdescribed may be prepared in quantity and stocked in coils in readinessfor 'the further steps converting them into individual blades.

These and other features of my invention will best be understood andappreciated from the following description of its application to themanufacture of a blade strip for use in the manufacture of safety razorblades as illustrated in the accompanying drawing in which:

Fig. 1 is a view in longitudinal section, somewhat diagrammatic incharacter, of one form of apparatus which may be used in carrying outthe method ofmy invention in which the blade strip is shown in thenitriding step.

Fig. 2 is a view in perspective of a portion of the blade strip.

Fig. 3 is a similar view of a finished blade.

In manufacturing safety razor blades by the method of-my inventionherein illustrated the blade blanks 10 are rst outlined in strip form.

' As shown in Fig. 2 this may be done by punching or dieing out suitableedge notches and perforations in a continuous strip or ribbon ofnitralloy or other nitridable alloy which may be secured commercially,rolled to the desired thickness. As herein shown each blade blank isprovided with an internal aperture 12 in the shape of a slotintersecting recesses, and with cut-out portions forming corner notches14 which, in the finished blade, obviate the possibility of cornerpressure from the cap of the razor. The strip may be scored or otherwisemarked to set off one blank from the next. These steps and thosefollowing being carried out upon the material in continuous strip form.

The material employed in the strip .described above may be selected asalready intimated. Either of the following analyses are satisfactory.

Analysis Analysis Element A B Carbon 36 23 Stimm il 'it B011 Y Aluminuml. 23 1. 24 Chromium l. 49 l. 58 Snlnhnr 010 011 Phosphnrna .013 011Molybdenum 18 20 In those cases where the blade strip is protected fromthe nitriding action between' its marginal edges by a coating orplating, I have found nonferrous metals such as tin, copper, silver,nickel, chromium, and possibly others, to be effective. Accordingly inthe accompanying drawing the blade strip is shown as having platedsurfaces which are terminated-at each margin of the strip by a groundbevel which exposes the ferrous alloy.

Preferably astrip may be prepared by electroplating itsentire surface,together with its exterior marginal edges and interior edges of the4apertures 12 and then having the plating removed by grinding along itsmarginal edges.

Having prepared the blade strip in the manner above outlined, it isready for the nitriding operation which may be effectively carried outby apparatus which will now be described.

The apparatus comprises, broadly, an elongated heated chamber, orfurnace liquid sealed at each end and provided internally with guidesfor the tensioned blade strip, together with means for admitting anddischarging ammonia gas to theI heated and tensioned strip. The furnacecomprises a horizontally disposed pipe 20 pro'- vided at either end witha special cast fitting or elbow 22, each directed downwardly at an angleof substantially 45.- Each of the fittings 22 is provided with an idle"guide roll 24 disposed so as to direct the blade strip, which as awhole is in- 34 carrying a roller 36 and having suspended from its endsa yoke 38 with a downwardly extending stem upon which is supported aweight 40. The fitting 22 at the right hand or discharging end of thefurnace is provided with the downwardly extending pipe 42 bevelled atits lower end and extending beneath oil 28 in a tank 44. The tank 44 isprovided with journal bearings for a roll 46 whichwis maintained in afixed position entirely submerged by the oil.

The blade strip 16 is delivered to the roll 36 at the entering end ofthe apparatus from a pair,

of positively driven feed rolls 50 which advance the blade strip at adefinite uniform rate. Upon leaving the tank 44 at the delivering end ofthe apparatus the blade strip is fed between two similar positivelydriven feed rolls 52 which are operated to deliver the blade strip fromthe apparatus at the same rate at which it is delivered thereto. Thelength of the strip maintained between the two sets of feed rollers isregulated so that the weighted roll 36 will be at all times suspendedfrom it, and the entire blade strip between the feed rolls will thus bemaintained under a uniform'and controllable degree of tension. This maybe regulated, as may be apparent, by reducing or increasing the size ofthe weight 40. The blade strip is thus stretched tightly between theguide rolls 24 and in the portion of its path between these guide rollsand the feed rolls at either end of the apparatus. Moreover, since therolls are all of plain cylindrical shape the blade strip is flattened byits contact with them.

The feeding and tensioning of the blade strip has now been described.The heating thereof is effected in the apparatus illustrated byencircling the pipe 20 with a coil of resistance wire 54 embedded orcovered with insulating material 56. By the passage of an electriccurrent through this coil the pipe 20 may be heated to any desiredtemperature and maintained uniformly thereat. A temperature of 950 F. to1400'F. for the interior of the pipe, 20 has been found satislfactory inpractice and permits the blade strip It should be pointed out inconnection with the apparatus above described that the pipe may be ofany convenient length and that it forms a very effective container forammonia in contact Vwith the blade strip being treated. This isparticularly advantageous from the standpoint of economy. in that thewaste of ammonia by dissooiation on account of contact with heated areasis reduced tc a minimum while the ammonia supplied to the apparatus isutilized to mammum eiect in connection with the blade strip.

It should be further pointed out that the apparatus herein disclosed,and the method of its use, permits considerable flexibility, andconsequently are useful in producing blade strips of dieringcharacteristics. For example, the rate of ieed of the blade stripthrough the apparatus may be varied within wide limits so that thelength of the nitriding process may be regulated in this manner. Again,the temperature of the pipe 20 may be regulated so that the heat atwhich the nitriding process takes place may be varied to produce anydesired eiect. As a general thing, and between definite limits, the

higher the temperature and the longer the operation, the greater thevolumeY of nitrided material produced. As indicating a workable range,it may be stated that a nitriding operation at a temperature of 1100 F.extended for e. period of l5 minutes will ordinarily nitride and hardenthe marginal edges of a blade strip sufficient for the manufacture ofrazor blades.

Having thus described my invention what Iv claim as new and desire tosecure by Letters Patent of the United States is' Y l. The method ofmanufacturing blades having nitrided cutting edges, characterized by thesteps of subjecting a longitudinal zone ins strip of nitridable ferrousalloy to the combined action of heat and ammonia, thereby nitriding thestrip in said zone. and simultaneously maintaining the strip underlongitudinal tension theby substantieliy reducing distortion in thestrip during the nitridlng operation. y

2. The method ci manufacturing blades having nitrided cutting edges,characterized by the steps of tensioning a strip of nitridable ferrousalloy, and nitriding longitudinally disposed portions thc-erect` whilethe strip is maintained under tension, thereby substantially eliminatingdistortion of the strip during the nitriding operation.

' s. The method of manufacturing blades having nitrided cutting edges,characterized by the steps of nrotecting a strip oi nitridable ferrousalloy between its marginal edges and simultaneously heating and treatingthe strip with ammonia while maintaining it under tension, thereby theunprotected edges ofthe strip Without distorting the strip.

4. The method o1' manufacturing blades having nitrided cutting edges,characterized by the steps o! plating the surtace'o a strip of anitridable ferrous alloy, beveling an edge thereof to expose said alloyin a narrow zone and simultaneously heating and treating the strip withammonia while maintaining it under tension, thereby nitriding thebeveled edges of the strip without distortion.

5. The method of manufacturing blades having nitrided cutting edges,characterized by the step of continuously moving a tensioned strip of aferrous nitridable alloy, protected between its marginal edges, througha heated ammonia container,

thereby nitriding the edges of the strip without substantial distortion.

6. The method of manufacturing blades having' nitrided cutting edges,characterized by the steps of flattening a strip of nitridable ferrousalloy at separated points in its length, tensioning the strip betweensaid points and subjecting a marginal portion of said tensioned strip tothe combined action of heat and ammonia, thereby nitriding the treatedportion of the strip while the latter is held flat against distortion.

7. The method of manufacturing blades having nitrided cutting edges,characterized by the steps or heating a strip of a ferrous nitridablealloy, tensioning the heated strip to a point below the elastic limit ofthe heated alloy at that temperature thereby maintaining the strip in aflat condition and then nitriding the marginal portions of the heatedand tensioned strip, thereby substantially eliminating distortion due tonitriding.

8. The method of manufacturing blades having nitrided cutting edges,characterized by the steps of outlining the blade blanks in the strip,protecting the surface oi the strip between its marginal edges from theaction of ammonia, heating the strip to between 950 degrees and 1400degrees Fahrenheit, tensioning the heated strip to a point belour theelastic limit oi the alloy at that temperature, and then nitriding theunprotected edges of the tensioned strip, thereby substan-v tiallyeliminating distortion due to nitriding.

9. The method of manuaturing blades having nitrided cutting edges,characterized by the steps of outlining the blade blanks and theapertures thereof in a strip of a ferrous nitridable alloy, plating saidstrip, rough grinding its edges to expose the alloy in narrow marginalzones, heating said strip while maintaining it under tension andsimultaneously subjecting it to the action of ammonia gas, therebynitriding the edges of the strip without distortion due to nitriding,finishing grinding theedges thus nitrided, and then separating the stripinto individual blades.

IHOMS H. FROST.

